Olefins, in particular, monounsaturated olefins and nonconjugated polyunsaturated olefins which may be straight chain, branch chain, cyclic, or a combination thereof, are often produced relatively readily as isomers which are not the most valuable isomers in commercial or industrial usage. The conversion of these isomers to provide at least the thermodynamic mixture of the theoretically available isomers wherein the double bond or double bonds are in different positions has therefore been a desirable goal.
Among the previously reported approaches to solution of this problem may be mentioned U.S. Pat. No. 3,671,597 to Kroll. Kroll utilizes group VIII transition metals absorbed on certain metal oxide or metaloid oxide carriers to effect isomerization of terminal aliphatic olefins. The range of temperature at which the isomerizations are carried out are disclosed as lying between 100 and 200 degrees C.
Lisichkin, et al (Zh. Fiz. Khim. 1972, 46, 1056) report that certain "hydrides" specifically Ti, Zr, Hf, TiH.sub.2, ZrH.sub.2, and HfH.sub.2 will convert 1-hexene to 2-hexene and 3-hexene. This work indicates that in the case of zirconium and hafnium there is substantially no isomerization below 350 degrees and in the case of titanium a graph indicates a 30% isomerization at about 200 degrees rising to a peak of about 70% at about 350 degrees. Full evaluation of the significance of Lisichkin's work is difficult since titanium, zirconium and hafnium are known to be tetra valent and the exact meaning of the "hydrides" discussed in the paper is therefore not clear. Furthermore, there is no disclosure as to how the "hydrides" are prepared or how the 1-hexene is contacted with the catalyst.
In a related area, U.S. Pat. No. 4,125,567 to Kidwell and Lynch discuss the use of dicyclopentadienyl metal alkyls which cause the conversion of internal olefins to terminal olefins, a somewhat more specific aim than is intended by the present invention. It should also be noted that the catalyst organometallic reagent utilized by Kidwell is not a supported catalyst and therefore its separation from the reaction mixture is somewhat more cumbersome than would be the case in the use of supported catalysts.
The preparation of zirconium alkyls supported on a silica carrier as well zirconium hydrides similarly supported are disclosed by Zakharov, et al (J. Mol Cat. 2, 421, 1977) catalysts of this type are disclosed as being valuable for ethylene polymerization. There is no discussion by Zakharov, et al of any isomerization reactions although they do indicate (at page 431) and at page 434 that a bond between the zirconium and an olefin moiety does form and they further disclose that the thus coupled olefin moiety may be removed by the action of hydrogen to provide the corresponding supported zirconium hydride and the corresponding alkane. Methods for the formation of the aforementioned zirconium hydride silica supported catalysts may also be found in a paper by Candlin and Thomas (Adv. Chem. Ser., 132 212, 1974). Candlin and Thomas are concerned with polymerization and disproportionation and their work is not directed to isomerization.